Plant cells or explants are grown on artificial media using a method generally known as tissue culture. By this process cells derived from plants are grown in vitro, i.e., in an artificial medium under controlled conditions. The cells can be grown either in an aqueous suspension or in a suitable gel medium or grown attached to a solid support.
In general, cells of plants and explants have been grown using generally known tissue culture methods. It is desired to culture plant cells or explants in such an artificial medium, and to obtain increased cell multiplication and differentiation and development of plant embryo structures, which are progenitors of whole plants. This process of plant embryo development is called somatic embryogenesis.
In the past, it has been possible to culture explants of many higher plants on an artificial nutrient medium. A cluster of cells develop under appropriate conditions on the surface of the explant. This cluster of cells is called a callus. Cells from the callus can be transferred to a liquid culture medium.
The plant cells can maintain their metabolic processes if proper plant cell culture conditions are maintained. The cells must be provided adequate source of required nutrients and oxygen. One of the suitable plant tissue culture media is referred to as a Murashige-Skoog medium. It is described by T. Murashige and F. Skoog in Physiol. Plant. 15:473-497 (1962). The culture can conventionally be maintained in a liquid state with agitation, which can be varied as required. The plant cells must be transferred to fresh culture medium periodically to maintain the vigor and growth of the cells.
Embryogenesis is usually induced by manipulation of the plant growth regulator component or, at times, other components of the culture.
Such tissue culture using many higher plant cells, including cells of many important plants, results in no somatic embryos or a low yield thereof.
It is important to obtain significant somatic embryogenesis in a tissue culture process. Tissue culture is a powerful method for propagating certain elite and engineered genotypes as well as more standard ones. It is also highly useful for screening large numbers of plants for desired genetic variants of those plants. One of the shortcomings in the current state of the art is to obtain in a large number of important higher plants a sufficiently large yield of the embryos on a controlled basis. In the past, there has been some success in obtaining multiplication of cells, but the degree of success has been limited in the differentiation of those multiplied cells necessary to obtain effective yields of desired embryos, which then can mature into full plants.
Therefore, it is important to develop a new higher plant cell tissue culture process by which more effective somatic embryogenesis is provided. It is also important to provide a good yield of embryos in the process.
It would also therefore be important to develop plant tissue cultures which would provide a high degree of cell multiplication and differentiation to result in effective somatic embryogenesis by use of a stimulating material to be incorporated into such desired plant tissue cultures.
It has been found that by cell culture processes that production of certain desired plant metabolites such as shibolin have been realized. Shibolin is a useful compound having medicinal as well as pigment properties. Often such chemical metabolites are produced in large measure during a particular stage of plant development. If the development of the culture can be manipulated under controlled conditions using certain culture procedures, it would be possible to produce large quantities of such chemical metabolites efficiently. This would allow production of chemicals from plants not native to particular growing regions where it is desired to produce the chemicals.
By means of effective plant cell culture processes, it would be an important development to be able to produce effectively identical plants from an individual plant specimen by means of improved tissue culture process and by use of a new tissue culture. It would be further important to obtain such plants in good yield. Such a new process would enable the growth of plants which are much more true to original plant specimen than those obtained by growing plants from seeds of the particular plant specimen.